1. Field of the Invention
The present invention relates to an optical module used for the reception and transmission of a light signal in an optical communication.
2. Description of Related Art
FIG. 11 is an upper view showing an optical configuration of a transmission-reception unity type of optical module corresponding to a first prior art. A travelling direction of each light signal is indicated by arrows.
As shown in FIG. 11, an optical module is composed of a for-transmission laser diode 102 (sometimes called LD) for outputting a transmission-light signal of a 1.3 xcexcm wavelength band;
an optical fiber 103 for receiving a reception-light signal of a 1.5 xcexcm wavelength band from an outside and transmitting the transmission-light signal output from the for-transmission laser diode 102 to the outside;
an optical waveguide 101, having a first end surface 101a facing on both the for-transmission laser diode 102 and the optical fiber 103 and a second end surface 101b, for transmitting the transmission-light signal output from the for-transmission laser diode 102 and the reception-light signal output from the optical fiber 103; and
a for-reception photodiode 105 (sometimes called PD), acing on the second end surface 101b of the optical waveguide 101, for receiving the reception-light signal transmitting through the optical waveguide 101.
The optical waveguide 101 is composed of a first core 112, of which one end faces on the for-reception laser diode 102, for transmitting the transmission-light signal of the 1.3 xcexcm wavelength band output from the for-transmission laser diode 102;
a second core 113, of which one end faces on the optical fiber 103 and of which the other end is connected with the other end of the first core 112 at a connection point 115, for transmitting the reception-light signal received in the optical fiber 103;
a wavelength division multiplexing (WDM) filter 104, which is arranged in a groove formed in the optical waveguide 101 and on which the connection point 115 is positioned, for imperfectly reflecting the transmission-light signal transmitting through the first core 112 to the second core 113 to transmit the transmission-light signal to the outside through the second core 113 and the optical fiber 103 and passing the reception-light signal transmitting through the second core 113 and a portion of the transmission-light signal transmitting through the first core 112;
a third core 114, of which one end faces on the other ends of the first and second cores 112 and 113 and the other end 114a faces on the for-reception photodiode 105, for transmitting the reception-light signal and the portion of the transmission-light signal passing through the WDM filter 104 and sending the reception-light signal and the portion of the transmission-light signal to the for-reception photodiode 105; and
a cladding body 116 surrounding the first core 112, the second core 113, the third core 114 and the WDM filter 104.
The for-reception PD 105 is positioned on a prolonged line of the third core 114 and is arranged in the neighborhood of the end 114a of the third core 114. The end 114a of the third core 114 denotes a light outputting position from which the reception-light signal transmitting through the second core 113 and passing through the WDM filter 104 are output.
In the above configuration, an operation of the optical module is described.
A transmission-light signal of a 1.3 xcexcm wavelength band emitted from the for-transmission LD 102 transmits through the first core 112 and is reflected by the WDM 104 to the second core 113, and the transmission-light signal is coupled with the optical fiber 103. Therefore, the transmission-light signal is output to the outside.
Also, a reception-light signal of a 1.5 xcexcm wavelength band, which is transmitted from the outside and is received in the optical fiber 103, transmits through the second and third cores 113 and 114 while passing through the WDM filter 104, and the reception-light signal is detected in the for-reception PD 105.
Therefore, an optical communication can be performed between the side of the optical module and the outside.
In this case, because the transmission-light signal is not perfectly reflected by the WDM 104, a portion of the reception-light signal undesirably passes through the WDM 104 and the third core 114 and is detected in the for-reception PD 105.
FIG. 12 is an upper view showing an optical configuration of a transmission-reception unity type of optical module corresponding to a second prior art. A travelling direction of each light signal is indicated by arrows.
As shown in FIG. 12, an optical module is composed of a for-transmission laser diode 122 (sometimes called LD) for outputting a transmission-light signal of a 1.3 xcexcm wavelength band;
an optical fiber 123 for receiving a reception-light signal of a 1.5 xcexcm wavelength band from an outside and transmitting the transmission-light signal output from the for-transmission laser diode 122 to the outside;
an optical waveguide 121, having a first end surface 121a facing on both the for-transmission laser diode 122 and the optical fiber 123 and a second end surface 121b, for transmitting the transmission-light signal output from the for-transmission laser diode 122 and the reception-light signal output from the optical fiber 123; and
a for-reception photodiode 125 (sometimes called PD), facing on the second end surface 121b of the optical waveguide 121, for receiving the reception-light signal transmitting through the optical waveguide 121.
The optical waveguide 121 is composed of a first core 132, of which one end faces on the for-reception laser diode 122, for transmitting the transmission-light signal of the 1.3 xcexcm wavelength band output from the for-transmission laser diode 122;
a second core 133, of which one end faces on the optical fiber 123 and of which the other end is connected with the other end of the first core 132 at a connection point 134, for transmitting the reception-light signal received in the optical fiber 123;
a WDM filter 124, which is arranged on the second end surface 121b of the optical waveguide 121 and on which the connection point 134 is positioned, for imperfectly reflecting the transmission-light signal transmitting through the first core 132 to the second core 133 to transmit the transmission-light signal to the outside through the second core 133 and the optical fiber 123 and passing the reception-light signal transmitting through the second core 133 and a portion of the transmission-light signal transmitting through the first core 132; and
a cladding body 135 surrounding the first core 132, the second core 133 and the WDM filter 124.
The for-reception PD 125 is positioned on a prolonged line of the second core 133 and is arranged in the neighborhood of the connection point 134 connecting the first and second cores 132 and 133. The connection point 134 denotes a light outputting position from which the reception-light signal transmitting through the second core 133 and passing through the WDM filter 124 are output.
In the above configuration, an operation of the optical module corresponding to the second prior art is described.
A transmission-light signal of a 1.3 xcexcm wavelength band emitted from the for-transmission LD 122 transmits through the first core 132 and is reflected by the WDM 124 to the second core 133, and the transmission-light signal is coupled with the optical fiber 123. Therefore, the transmission-light signal is output to the outside.
Also, a reception-light signal of a 1.5 xcexcm wavelength band, which is transmitted from the outside and is received in the optical fiber 123, transmits through the second core 133 and the WDM filter 124, and the reception-light signal is detected in the for-reception PD 125.
Therefore, an optical communication can be performed between the side of the optical module and the outside.
In this case, because the transmission-light signal is, not perfectly reflected by the WDM 124, a portion of the reception-light signal undesirably passes through the WDM 124 and is detected in the for-reception PD 125.
As described above, though a main portion of the transmission-light signal of the 1.3 xcexcm wavelength band is reflected by the WDM filter 104 (or 124), the remaining portion of the transmission-light signal transmits through the WDM filter 104 (or 124). The transmission degree of the transmission-light signal depends on the performance of the WDM filter 104 (or 124).
Also, the for-reception PD 105 (or 125) is normally sensitive to both the transmission-light signal of the 1.3 xcexcm wavelength band and the reception-light signal of the 1.5 xcexcm wavelength band. Therefore, the remaining portion of the transmission-light signal, which is emitted from the for-transmission LD 102 (or 122) and transmits through the first core 112 (or 132), transmits through the WDM filter 104 (or 124), and the remaining portion of the transmission-light signal is detected with the reception-light signal by the for-reception PD 105 (or 125).
Accordingly, because the remaining portion of the transmission-light signal transmits through the WDM filter 104 (or 124), an optical cross-talk based on the mixture of the transmission-light signal with the reception-light signal occurs in the for-reception PD 105 (or 125). Therefore, the reduction of an optical cross-talk is limited to a value ranging from 40 dB to 50 dB, so that there is a drawback that the optical communication cannot be performed at a sufficiently high quality.
Also, a portion of the transmission-light signal emitted from the for-transmission LD 102 (or 122) transmit through a cladding body surrounding the cores and/or a substrate of the optical waveguide 101 (or 121) as stray light. Therefore, the stray light transmitting through the cladding body and/or the substrate is undesirably detected in the for-reception PD 105 (or 125), so that an optical cross-talk based on the mixture of the stray light with the reception-light signal occurs in the for-reception PD 105 (or 125).
An object of the present invention is to provide an optical module in which an optical communication is performed while reducing an optical cross-talk based on the mixture of a transmission-light signal with a reception-light signal or/and an optical cross-talk based on the mixture of stray light with a reception-light signal.
The object is achieved by the provision of an optical module, comprising:
transmission-light signal emitting means for emitting a transmission-light signal having a first wavelength band;
an optical fiber for receiving a reception-light signal having a second wavelength band from an outside and transmitting the transmission-light signal emitted from the transmission-light signal emitting means to the outside;
an optical waveguide for transmitting the transmission-light signal emitted from the transmission-light signal emitting means and the reception-light signal received by the optical fiber, giving a first travelling direction characteristic corresponding to a first direction to the reception-light signal and outputting the transmission-light signal to the optical fiber to transmit the transmission-light signal to the outside;
light transmitting means, extending in the first direction at a first end facing on the optical waveguide, for receiving the reception-light signal having the first travelling direction characteristic from the optical waveguide at the first end and transmitting the reception-light signal; and
reception-light signal detecting means for detecting the reception-light signal transmitting through the light transmitting means,
wherein the optical waveguide comprises
a first core, having a first end facing on the transmission-light signal emitting means and a second end and extending in a second direction differing from the first direction at the second end, for transmitting the transmission-light signal received at the first end, giving a second travelling direction characteristic corresponding to the second direction to the transmission-light signal and outputting the transmission-light signal from the second end;
a second core, connected with the second end of the first core at a connection point, for transmitting the reception-light signal; and
a main filter, on which the connection point is placed, for reflecting a major portion of the transmission-light signal received at the connection point from the first core to the second core to output the major portion of the transmission-light signal from the optical fiber to the outside, transmitting the remaining portion of the transmission-light signal received at the connection point from the first core and the reception-light signal received at the connection point from the second core and sending the reception-light signal of the first travelling direction characteristic to the light transmitting means to make the reception-light signal detecting means detect the reception-light signal, while preventing the remaining portion of the transmission-light signal of the second travelling direction characteristic from being sent to the light transmitting means.
In the above configuration, because a first travelling direction characteristic is given to a reception-light signal received at the optical fiber from the outside when the reception-light signal transmits through the second core and the main filter of the optical waveguide, the reception-light signal can transmit through the light transmitting means, so that the reception-light signal of the second wavelength band is detected by the reception-light signal detecting means.
In contrast, a transmission-light signal emitted from the transmission-light signal emitting means transmits through the first core of the optical waveguide, and a second travelling direction characteristic is given to the transmission-light signal. Thereafter, a major portion of the transmission-light signal is reflected to the second core by the main filter and is output from the optical fiber to the outside. Also, the remaining portion of the transmission-light signal having the second travelling direction characteristic transmits through the main filter. In this case, because the transmission-light signal has the second travelling direction characteristic, the transmission of the remaining portion of the transmission-light signal to the light transmitting means is prevented. Therefore, the transmission-light signal is not detected by the reception-light signal detecting means.
Also, a portion of the transmission-light signal emitted from the transmission-light signal emitting means transmits as stray light through an area of the optical waveguide other than the first and second cores, and the stray light transmits through the main filter. Assuming that the light transmitting means is not arranged between the optical waveguide and the reception-light signal detecting means, the stray light is undesirably detected by the reception-light signal detecting means. However, because the light transmitting means is arranged between the optical waveguide and the reception-light signal detecting means and because the stray light does not have the first travelling direction characteristic, the stray light does not transmit through the light transmitting means, so that the stray light is not detected by the reception-light signal detecting means.
Accordingly, because the second travelling direction characteristic is given to the transmission-light signal by the first core and because a light signal having the first travelling direction characteristic is selectively received by the light transmitting means, the detection of the transmission-light signal by the reception-light signal detecting means is prevented, and an optical cross-talk based on the mixing of the transmission-light signal with the reception-light signal can be prevented.
Also, because the first travelling direction characteristic is not given to the stray light and because a light signal having the first travelling direction characteristic is selectively received by the light transmitting means, the detection of the stray light by the reception-light signal detecting means is prevented, and an optical cross-talk based on the mixing of the stray light with the reception-light signal can be prevented.
It is preferred that the optical waveguide further comprises a third core for receiving a minor portion of the transmission-light signal obtained from the remaining portion of the transmission-light signal transmitting through the main filter, receiving the reception-light signal transmitting through the main filter and transmitting the minor portion of the transmission-light signal and the reception-light signal, the reception-light signal being sent to the light transmitting means to make the reception-light signal detecting means detect the reception-light signal while preventing the other minor portion of the transmission-light signal, which is obtained from the remaining portion of the transmission-light signal and is not received by the third core, from being sent to the light transmitting means.
In this optical waveguide, the reception-light signal transmitting through the main filter and the third core is sent to the light transmitting means and is detected by the reception-light signal detecting means. In contrast, after the remaining portion of the transmission-light signal transmits through the main filter, a minor portion of the transmission-light signal obtained from the remaining portion of the transmission-light signal transmits through the third core, and the other minor portion of the transmission-light signal obtained from the remaining portion of the transmission-light signal does not transmit through the third core but transmits as stray light through an area of the optical waveguide other than the third core. because the stray light does not have the first travelling direction characteristic, the stray light does not transmit through the light transmitting means, so that the stray light is not detected by the reception-light signal detecting means.
Accordingly, the transmission of the other minor portion of the transmission-light signal to the light transmitting means is prevented, and the detection of the transmission-light signal by the reception-light signal detecting means is reduced to a minimum. Therefore, an optical cross-talk based on the mixing of the transmission-light signal with the reception-light signal can be reduced to a minimum, and an optical cross-talk based on the mixing of the stray light with the reception-light signal can be prevented.
It is preferred that the second core extend in the first direction at the connection point to give the first travelling direction characteristic corresponding to the first direction to the reception-light signal in the second core.
Because the first travelling direction characteristic is given to the reception-light signal, the reception-light signal can transmit through the light transmitting means, so that the reception-light signal can be selectively detected by the reception-light signal detecting means while preventing the transmission-light signal of the second travelling direction characteristic from being detected by the reception-light signal detecting means.
It is also preferred that the optical waveguide further comprises:
a first transparent resin body, filling up a space from a light emitting point placed on the main filter of the optical waveguide to a light incident end of the light transmitting means, for transmitting the reception-light signal output from the light emitting point of the main filter to the light incident end of the light transmitting means;
a second transparent resin body, filling up a space from a light emitting end of the light transmitting means to the reception-light signal detecting means, for transmitting the reception-light signal output from the light emitting end of the light transmitting means to the reception-light signal detecting-means; and
an opaque resin body, arranged in a space surrounding a light propagation route from the light emitting point of the main filter to the reception-light signal detecting means through the light transmitting means, for preventing flight transmitted from a surrounding area of the optical module or stray light transmitting through the optical waveguide from being detected by the reception-light signal detecting means.
In this optical module, the opaque resin body shields the space surrounding the light propagation route from light transmitted from a surrounding area of the optical module or stray light transmitting through the optical waveguide. Also, the reception-light signal transmits through the light propagation route while passing through the first and second transparent resin bodies.
Accordingly, an optical cross-talk based on the mixing of the light or the stray light with the reception-light signal can be prevented.
It is also preferred that the optical module further comprises:
a light shielding film, arranged on a light emitting end surface of the optical waveguide except for an area of the third core, for shielding the light transmitting means and the reception-light signal detecting means from stray light transmitting through an area of the optical waveguide other than the third core.
It is also preferred that the optical module further comprises:
a light shielding film, arranged on a light emitting surface of the main filter except for a portion corresponding to the connection point of the first and second cores, for shielding the light transmitting means and the reception-light signal detecting means from stray light transmitting through the optical waveguide other than the first and second cores.
In these optical modules,.because the light shielding film prevents stray light transmitting through the optical waveguide from being leaked from the optical waveguide, the stray light is not detected by the reception-light signal detecting means. Accordingly, an optical cross-talk based on the mixing of the stray light with the reception-light signal can be moreover prevented.
It is also preferred that the optical module further comprises:
a supplementary filter, arranged on an end surface of the optical waveguide facing on the light transmitting means, for reflecting the minor portion of the transmission-light signal transmitting through the third core of the optical waveguide and transmitting the reception-light signal transmitting through the third core of the optical waveguide.
In this optical module, the supplementary filter prevents the minor portion of the transmission-light signal from transmitting through the light transmitting means and transmits the reception-light signal to the light transmitting means. Accordingly, the optical cross-talk based on the mixing of the transmission-light signal with the-reception-light signal can be prevented.
It is also preferred that the optical module further comprises:
a first transparent resin body, filling up a space from a light emitting point placed on a light emitting end surface of the optical waveguide to a light incident end of the light transmitting means, for transmitting the reception-light signal output from the light emitting point of the supplementary filter to the light incident end of the light transmitting means;
a second transparent resin body, filling up a space from a light emitting end of the light transmitting means to the reception-light signal detecting means, for transmitting the reception-light signal output from the light emitting end of the light transmitting means to the reception-light signal detecting means; and
an opaque resin body, arranged in a space surrounding a light propagation route from the light emitting point of the supplementary filter to the reception-light signal detecting means through the light transmitting means, for preventing light transmitted from a surrounding area of the optical module or stray light transmitting through the optical waveguide from being detected by the reception-light signal detecting means.
In this optical module, the opaque resin body shields the space surrounding the light propagation route from light transmitted from a surrounding area of the optical module or stray light transmitting through the optical waveguide. Also, the reception-light signal transmits through the light propagation route while passing through the first and second transparent resin bodies. Accordingly, an optical cross-talk based on the mixing of the light or the stray light with the reception-light signal can be moreover prevented.
It is also preferred that the optical module further comprises:
a light shielding film, arranged on a light emitting surface of the supplementary filter except for a portion corresponding to the third core of the optical waveguide, for shielding the light transmitting means and the reception-light signal detecting means from stray light transmitting through the optical waveguide other than the third core.
In this optical module, because the light shielding film prevents stray light transmitting through the optical waveguide other than the third core from being leaked from the optical waveguide, the stray light is not detected by the reception-light signal detecting-means. Accordingly, an optical cross-talk based on the mixing of the stray light with the reception-light signal can be moreover prevented.
It is also preferred that the optical module further comprises:
a first transparent resin body, filling up a space from a light emitting point placed on the main filter to a light incident end of the light transmitting means, for transmitting the reception-light signal output from the light emitting point of the main filter to the light incident end of the light transmitting means;
a second transparent resin body, filling up a space from a light emitting end of the light transmitting means to the reception-light signal detecting means, for transmitting the reception-light signal output from the light emitting end of the light transmitting means to the reception-light signal detecting means; and
an opaque resin body, arranged in a space surrounding a light propagation route from the light emitting point of the main filter to the reception-light signal detecting means through the light transmitting means, for preventing light transmitted from a surrounding area of the optical module or stray light transmitting through the optical waveguide from being detected by the reception-light signal detecting means.
In this optical module, the opaque resin body shields the space surrounding the light propagation route from light transmitted from a surrounding area of the optical module or stray light transmitting through the optical waveguide. Also, the reception-light signal transmits through the light propagation route while passing through the first and second transparent resin bodies. Accordingly, an optical cross-talk based on the mixing of the light or the stray light with the reception-light signal can be moreover prevented.
It is also preferred that the optical module further comprises:
a light shielding film, arranged on a light emitting surface of the main filter except for a portion corresponding to the connection point of the first and second cores, for shielding the light transmitting means and the reception-light signal detecting means from stray light transmitting through the optical waveguide.
In this optical module, because the light shielding film prevents stray light transmitting through the optical waveguide from being leaked from the optical waveguide, the stray light is not detected by the reception-light signal detecting means. Accordingly, an optical cross-talk based on the mixing of the stray light with the reception-light signal can be moreover prevented.
It is also preferred that the optical module further comprises:
a supplementary filter, arranged on a light incident end and/or a light emitting end of the light transmitting means, for reflecting light having the first wavelength band and transmitting the reception-light signal received from the main filter of the optical waveguide.
In this optical module, even though the remaining portion of the transmission-light signal intends to transmit through the light transmitting means, the supplementary filter prevents light having the first wavelength band from transmitting through the light transmitting means or being output to the reception-light signal detecting means and transmits the reception-light signal to the light transmitting means. Accordingly, the optical cross-talk based on the mixing of the transmission-light signal with the reception-light signal can be moreover prevented.
It is also preferred that the optical module further comprises:
a light shielding film, arranged on a light emitting surface of the light transmitting means except for a core portion of the light transmitting means, for shielding the reception-light signal detecting means from light transmitting through a cladding portion of the light transmitting means.
In this optical module, because the light shielding film shields the reception-light signal detecting means from the light transmitting through the cladding portion of the light transmitting means, the light is not detected by the reception-light signal detecting means. Accordingly, an optical cross-talk based on the mixing of the light transmitting through the cladding portion of the light transmitting means with the reception-light signal can be prevented.